Since 1997, Eiichiro Oda has produced One Piece. According to a recent Japanese magazine article, he has zero days off. And every night, he gets around four hours of sleep on average.

One Piece is the most popular manga in Japan. Initially, Oda planned to end One Piece sooner (after five years of serialization), but the manga, now in its 15th year, has become a cultural juggernaut.

If the 37-year-old manga artist does ever end the comic, he'll retire. "If I stop drawing One Piece," Oda recently said, "I'm thinking I'll quit being a manga artist."

Continuing, he said, "To be precise, this isn't going to be serialized for a long time, and that I swear on my heart." What's keeping him going, Oda said, is that he's thinking of the work he'll leave behind after he's dead.